Surface-immobilized polyampholytic silver nanoparticles for SERS detection of cations and anions in aqueous solutions
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A new procedure was used for the preparation of stable silver colloids by reduction of silver nitrate with (N-(2-hydroxyethyl) piperazine-N-2-ethanesulfonic acid (HEPES). The nanoparticle size and the surface charge could be tuned by changing the initial pH of a HEPES solution. Rhodamine 60 and NaSCN were used respectively as model cationic and anionic analytes to study the effect of surface charge of the silver colloids on detection sensitivity. The silver colloids exhibit SERS activity comparable to those obtained by the popular Lee-Meisel approach. The combination of the high SERS sensitivity and the ability to control the nature of surface charge renders HEPES-reduced polyampholytic silver colloids a potentially powerful platform for sensing and detection of both cations and anions in aqueous solutions.